1. Field of the Invention
This invention relates to an electronic system for controlling the air-fuel mixture in an internal combustion engine and more particularly to a closed loop system for maintaining a desired air-fuel mixture in an internal combustion engine wherein the operator commands a given fuel flow and the control system adjusts air flow to maintain the desired air-fuel ratio.
2. Description of the Prior Art
In recent years, the importance of maintaining a desired or optimal air-fuel ratio in an internal combustion engine has been increasingly emphasized. Recent health and safety concerns aimed at lowering or eliminating pollution and the like have been enacted into federal, state and local laws regulating emission standards. Today's internal combustion engines, such as those used in automobiles and the like, must conform to those standards and must, under substantially all operating conditions, generate and emit no more than a predetermined amount of air pollutants such as carbon monoxide, noncombustible hydrocarbons, and various oxides of nitrogen.
Experience has shown that for each internal combustion engine, and for each set of conditions under which that engine operates, there exists certain desired air-fuel ratios which must be maintained for insuring optimal control over the generation and emission of pollutants. Similarly, it has been found that there also exists, for a given engine and for a given set of engine operating conditions, optimal air-fuel ratios which produce optimal drivability. Recent fuel shortages and the ever-increasing cost of fuel has caused increased concern, and more recently legislation has been enacted setting various miles per gallon standards for automobiles.
Therefore, the number of miles per gallon is one important aspect of drivability and another aspect relates to how responsive the internal combustion engine is to operator commands without stalling, sputtering, or producing engine roughness and the like.
Unhappily, there is, in many cases, a direct conflict between the optimal air-fuel ratio required for maintaining the minimal generation and emission of pollutants and the air-fuel ratio required for maintaining optimal drivability. Therefore, modern engines are usually required to select an air-fuel ratio which conforms to all regulations governing the generation and emission of pollutants while providing the optimal drivability possible under such circumstances.
In most internal combustion engines, an accelerator is provided which can be selectively positionable by the operator to command a given air flow by selectively positioning a throttle valve and then fuel is metered into the engine by any of several methods, as by carburators or fuel injectors or the like. In most systems designed for maintaining a predetermined air-fuel ratio, for example in U.S. Pat. No. 3,750,632 for an "Electronic Control for the Air-Fuel Mixture and for the Ignition of an Internal Combustion Engine," the quantity of metered or injected fuel is varied to maintain the desired air-fuel ratio. Such systems have many inherent problems including the need for some system of providing acceleration enrichment when the internal combustion engine is accelerating or some type of fuel enrichment during initial start and engine warm-up.
Relatively few systems, such as that shown in U.S. Pat. No. 3,983,848 for a "Fuel Injection System" allow the operator to command a given fuel flow and then control the flow of air to maintain a predetermined air-fuel ratio and most such systems require rather expensive and complex means for sensing the actual air flow in the engine intake and do not use some form of negative feed-back for correcting air flow to obtain a more precise control over the desired or optimal air-fuel ratio.
Still other systems, such as that illustrated in U.S. Pat. No. 3,738,341 for a "Device for Controlling the Air-Fuel Ratio in a Combustion Engine" are able to more accurately control air-fuel ratio by varying the quantity of injected fuel in accordance with a feed-back signal indicative of the level of carbon dioxide present in the exhaust system. While this is a relatively crude pollution control means, it does not possess the degree of sensitivity required for maintaining optimal drivability and the system must still provide some type of acceleration enrichment or the like.
The present invention does not require a separate acceleration enrichment system since it has inherent or automatic acceleration enrichment because the fuel flow commanded by the operator enters first and then the air flow increases.
The present invention avoids the problems and disadvantages of the prior art by providing a control system for selectively varying air flow in response to operator commanded fuel flow. Basic control is determined by various engine operating parameters including fuel flow and a closed loop system is provided for sensing a parameter indicative of the actual air-fuel mixture existing in the engine for adjusting or correcting the control to maintain the desired or optimal air-fuel ratio.